White cast iron alloy and method of making the same



. Patented Sept. 10, 1935 UNITED STATES PATENT OFFICE WHITE CAST IRONALLOY AND METHOD OF'MAKING THE SAME Frank A. Raven, Albany, and ClarenceD. Foulke,

Buiialo, N. Y.,

assignors to Industrial Furnace New York No Drawins.

Application January 15, 1932,

Serial No. 586,952

2 Claims. (01. 148-21.?)

This invention relates to alloys of white cast iron, and it hasparticular reference to a white iron alloy, containing, in addition tothe usual ingredients, alloying elements in such propor- 5 tions as torender the iron readily amenable to heat treatment to yield an articlehaving desirable physical properties.

Heretofore it has been the general practice to make white iron castingswith carbon and silicon,

lo and manganese and sulphur, in such proportions as. to yield, uponheat treatment, the material known as malleable cast iron. Suchmaterial, "as a commercial article, has been made with'a tensilestrength of something less, on the aver- 5' age, of 55,000 pounds persquare inch, with elongations of the order of twelve to twenty per centin two inches. Metallurgically, malleable cast iron is composed of freeiron or ferrite, interspersed with temper carbon. Aside from the Ifconstituents named above, phosphorus is also usually present, but otherimpurities have been avoided in general foundry practice.

The factors considered in the making of malle- I able castiron havebeen, that the carbon must be originally present as combined carbon, .orcementite, that the silicon must not be too'high, lest the criterion ofcombined carbon be defeated, albeit the silicon should be present inappreciable amounts to facilitate the subsequent breakdown of thecementite, or, in otherwords, to accelerate the annealing orgraphitizing action. These matters have led to certain limits and ratiosfor carbon. and silicon; thus, if the carbon be 2.45 per cent, thesilicon may be about 0.84 per cent, andifthe carbon be.2.10 per siliconshould be about 1.06 percent.

Likewise, the manganese and sulphur, both of which are knownas'retardants of the annealing process, should not be too high, lest theheat treatment be necessarily extended. Foundry practice, however, impomlimits on the sulphur, and the manganese value has been made somebeenfoimd that while these two elements,

' other. In practice, sulphur values of about 0.06 I to 0.10 per centhave been tolerated, with the manganese-running to about 0.3 per cent;the

conditions and thetypeofcastingdeslred.

It has more recently been discovered that, if the white iron casting ismodified in its composition to contain an available excess of retardant,

cent, the

what more than twice the'sulphur, it havingseparately, exert aretarding. eifect, in proper proportions .conjointly they neutralizeeach.

exact flgures'varyingrof course, with foundry as, for example, an excessof manganese, to

about say 0.6 to 1.5 per cent, and such castings are subjected tocertain heat treating operations,

it' is possible to obtain a commercial metal, differing materially frommalleable cast iron in its metallurgical aspect, as well as chemicalcom- 5 position, and also having greatly. enhanced physical properties.In the practice of this process, it has been observed that the time ofheat treatment of the white iron casting, neces: sary to effect thebreakdown of the free cementite, may run for an appreciable time, sayabout twenty-four hours at 1700 F. This length of time may beobjectionable for economic 'or commercial reasons. It has also beenobserved,

moreover, that the castings made by the process referred toare open tothe general objection of low corrosion resistance as compared tomallecreased resistance to corrosion, by alloying in the white ironcasting a combination of elements, which facilitate the breakdown offree cementite,-and so lessen the time of heat treatment required, butwhich combination does not, however, effect a like influence on thedecomposition ,of combined cementite or ,pearlite. In this connection,it may be explained that the conversion of hard andnon-ductile whiteiron into a more ductile and strong material is thought to be due to thedecomposition of the combined carbon or cementite. This cementite occursin two conditions, first, as free or massive cementite, which isdecomposed above certain temperature ranges, generally called thecritical. The

balance of the cementite occurs in the form of pearlite, which is brokendown by heat at-temperatures below the critical. Our invention ispredicated upon the principle of modifying theus normal white ironcomposition by the inclusion of elements which do not retard or preventthe actions occurring above the critical, but which do exert such effecton the actions below the critical, so that physical changes may takeplace so in preference to the chemical change which has been soughtheretofore in making malleable cast iron. The invention further involvesthe principle of utilizing, as the modifying means, ele-' ments'whichimpart to the coating, in its final iorm, enhanced physical propertiesand a greater resistance to corrosion.

' More specifically, we have discovered that ii the composition of theiron be modified by the addition of chromium and copper, the desiredresults may be obtained.

be noted that, heretofore, chromium has Men recognized as a retardantfor the annealing actions, and the eiiect oi chromium, when I present toany appreciable extent, is so marked that its presence is shunned by thewhite iron manufacturer or founder. Copper, on the other hand, has beenstated by some to be a retardant 1 oi the annealing operation, and byothers an accelerant, and published reports oi the addition of copperhave indicated that it is not emcacious'in increasing the strength oithe heat treated casting. Whatever may be the truth or merits of theseseveral views, we are able to utiline these elements. to advantage, iorwe have discovered that, at temperatures oi treatment above thecritical, the accelerating eiiect oi copper predominates, so that ashorter time oi heat treatment .may be employed, whereas, attemperatures below the critical, the accelerating eiiect oi cop-- perissominimiscdas'not tointeriere with the "preierential progress oi thephysical actions, desiredinimpartingtothecastingtheenhanced physicalproperties; We have iurther iound that this combi'nation'oi elementsimparts to the ilnal casting an increased resistance to corrosive ae-Inspeakingjustaboveoicoppenitwflhoicourse,beunderstoodthatreierenceismadetothceiiectoithecopperpresentwithotherelements,suchasthe retardantschromium-or manganese. IicopperaloneisemployedJt'appcars that theaccelerating influence prevails attemperatnresbothaboveandbelowtheeritimwhile li-chromium alone is used,the retarding eiiect issuchastorenderdiiilcultanyann fl latalL' 'lhe two"specifics, conjointly, however, well attain the object oi acceleratingthe high temperature reaction, without interiering with the lowtemperaturechangesdesiredtoobtaintheiinalprodnot herein contemplated.

As exernplaryoitheresultstobeobtained,the

'iollowingdata,derivediromthetestingoisample'barsoiwhitecastirommaybenoted.

'- lilloy A Ohuntaleomposltbn Nod AlloyNm! 2.0) an LIB. LG (ill 0-85 canam 0.07 0.47! 0.!) MIHapproa.)

8amplesoi-each alloyweresubjected aheat treatment at 1700' I". forperiods oi time oi 10,15, and 26 hours, theflast time being that whichwould be used (approximately) in the high temperature heat treatment oithis alloy, ii neither or copper were present, but it themanganesevaluewerehigh,asintheinstant cases. Microscopic examination oiAlloy No. 1 showed that the free cementitewas not broken down inany oithe three heats, thereby showing that, taken alone, or with the apronoimced retarding effect was obtained with the addition of chromium.'Alloy No. 2, however,

showed nearly complete breakdown of the mas-.

si've cementite, after heat treatment for only ten hours, therebyshowing that the addition of cop- In this connection, it,

a low temperature heat treatmentat 1300 F. for" 1 twenty hours, or thatwhich, with manganese present but chromium and copper absent, could beexpeoted'to givea material having aspheroidized structure withanultimatcstrength in the neighborhood oi 90,000 pounds. The values 15 obtainedwere, for Alloy No. 1, ultimate strength 86,100, yield point, 68,300,elongation 3.5 per cent. Theseflguresindicatethat theretardingeiiect oichromiumwasstill pronounced, sincethephysicalpropertiesarenotasmuchastheyshouldzo be, ii no chromium werepresent. With Alloy No. 2, the iollowing values were obtained, ultimate,91,000, yield point 69,600, elongati nine per cent, or about what couldbe anticipated ii neither chromium or copper were'present; These results25 7 indicate that the deleterious retardingeilect .oithechromium,takenaione,hadbeeneliminated, and,also,thattheundueaceeleratingeiiectoi LThemethodoimakinganiron irmnwhite which comps-mes iorming awhite Q fusion ior 5. length oi timesufllcient to decomposethe massivecementite andtodeveloptem-Tl tainingsilicon, manganese,

white iron with'an'excess of manganese to make amount of copper. I

the total manganese content between 0.6 and 1.5 per cent, said iron alsocontaining temper carbon 1 derivedfrom cementite but being substantiallytree from graphitic carbon andmassive oementlte, said ironiurthercontaining limited amounts of chromium and copper, the amount of copperbeing not more than two per cent and the amount of chromium being or theorder of one tenth the FRANK A. RAVEN.

CLARENCE D. 10

